This application pertains to the art of bonding or joining and more particularly to integrally bonding at least a pair of workpieces to each other.
The invention is particularly applicable to use with workpieces formed from a liquid phase system material such as cemented carbide, including cemented tungsten carbide and the like, and will be described with particular reference thereto. However, it will be appreciated that the invention has far broader applications and is deemed equally applicable to other types of liquid phase system materials.
Cemented carbide materials are formed into various shapes and configurations by techniques associated with the art of powder metallurgy. These techniques are well known and generally involve the process of consolidating metal powders into ingots or shaped parts without fusion or at least without fusion in the major portion of the powder components. Typically, the procedure involves pressing or compacting the powder into some desired shape and then heating or sintering the compact at a temperature below the melting point of its highest melting point constituent. It is known that cemented carbide pieces or members will stick to each other if placed in contact during the sintering operation.
It is often desired to fixedly interconnect a plurality of sintered carbide components to each other so as to define a subassembly or some finished article. Heretofore, such interconnections have been accomplished by several means including brazing and bonding under elevated temperature-pressure conditions. In such bonding, the temperature involved is approximately the same as that for sintering and the pressure is approximately in the range of 1000 psi or so. However, the resultant bonds were not entirely satisfactory and the process itself did not accommodate joining members which included intricate designs such as ducts, passages, grooves and the like.
One particular situation where the foregoing problems are apparent is in the manufacture of optical elements or mirrors which are utilized for high energy laser applications. The performance of high energy lasers is greatly influenced by the configuration of the optical elements involved. Small distortions of the optical surfaces may severely degrade the laser beam coherence and therefore, reduce its effectiveness. The mirrors themselves generally involve a configuration comprised of a plurality of components including a mirror surface or faceplate and a heat exchanger. These components include intricate configurations and/or relationships and must be fixedly secured to each other in the final mirror structure.
At the present time, mirrors and other optical elements for high energy laser applications are conventionally made from molybdenum. Such constructions are, however, approaching their limit of low distortion under high laser beam power density. Accordingly, it has been proposed to construct such mirrors from cemented tungsten carbide since it has about the same thermal conductivity as molybdenum, a lower coefficient of thermal expansion and a much higher modulus of elasticity. As a result, tungsten carbide is considered to be inherently better for low distortion mirror applications than molybdenum. However, to successfully manufacture or fabricate mirrors from the material adapted for laser applications, it has been necessary to develop a process or system whereby the various mirror components could be assembled into a monolythic structure free of flaws and distortion. The method or system should also readily accommodate joining components which include intricate designs without in any way damaging or impairing the designs during bonding or joining.
The subject invention provides a method or system which meets the foregoing needs and overcomes problems encountered with prior known bonding techniques employed for fixedly securing cemented carbide members to each other. In addition, and while application of the invention will hereinafter be specifically described with reference to a cemented tungsten carbide mirror construction, the invention is deemed broadly and equally applicable to joining or bonding other types of components or members formed from various liquid phase system materials adapted to use in other applications and/or environments.